The present invention relates to a method and apparatus for blending two or more different types of fibrous material, especially for intimately mixing several types of tobacco. More particularly, the invention relates to a novel and improved method and apparatus for blending different types of tobacco preparatory to processing of the resulting mixture in machines for the production of rod-shaped or other smokers' products.
It is often necessary to mix natural tobacco (such as whole leaves, rag, shreds of tobacco leaf laminae, fragments of ribs or stem, or a mixture of these) with reconstituted tobacco and/or with so-called expanded or puffed tobacco. A mixture which contains different types of tobacco must be homogeneous throughout in order to avoid undesirable fluctuations in taste from article to article, e.g., from cigarette to cigarette. In accordance with the presently prevailing practice, mixing of different types of tobacco is normally performed in rotating drums or in so-called blending boxes. Such apparatus are capable of forming acceptable mixtures; however, they invariably subject the particles of tobacco to substantial mechanical stresses with the result that the mixture contains a high percentage of short tobacco and/or tobacco dust. Particles of tobacco dust contaminate the plant and are likely to adversely affect the operation of highly sensitive equipment, such as testing devices which monitor the condition of wrappers of cigarettes, cigars or cigarillos and/or the density of tobacco-containing ends of rod-shaped smokers' products. Furthermore, pronounced mechanical stressing of tobacco particles is highly undesirable when the mixture which is to be homogenized contains sensitive expanded or puffed tobacco which is normally admitted to tobacco shreds in order to contribute to compactness of cigarette fillers without appreciable increase in the weight. Mechanical stressing of expanded tobacco is likely to reduce the volume of puffed particles with the result that the filler of a cigarette must contain a larger quantity of tobacco, i.e., of the most expensive component of a smokers' product.